Cartilage contains both in the chondrocytes and in the extracellular matrix a polypeptide growth factor which stimulates DNA synthesis and cell division in chondrocytes, Balb/c 3T3 and other cells. Current work in the laboratory is directed towards the purification of the growth factor from both normal and abnormal cartilage. We intend to investigate the role of the cartilage-derived growth factor in the growth of normal and abnormal chondrocytes both in vitro and in vivo by use of techniques such as cell culture and radioimmunoassay.